Backyard Aquaponics
A place to discuss aquaponics

This thread prompted me to GOMA and do a water test, the first in a month, since 22 June to be exact.

Two hours after feeding 20g of 7mm Spectra FF to 16 trout (approx 350g ea, so 0.35% by weight):
Water volume: 850L
Min Water Temp since last test: 12C
Max Water Temp since last test: 18C
Water Temp now: 16C
pH: 6.2
Ammonia: 0.25ppm
Nitrites: 0.0ppm
Nitrates: 20ppm

Seasol added since last test: None
Chelated iron added since last test: 5 teaspoons

Plant growth since last test: Excellent, we've had some sunshine and thinned out some of the larger (shading) plants.
Fish growth since last test: Good (subjective)
Pests, bugs, disease since last test: None significant


The fish were fed more than "normal" yesterday (50g vs 20g) so it's not unexpected they wont take much food today. I am considering increasing the feed to 30g per day, if they want it. Will wait and see what happens in the next week or so.


Scott

would you also have to factor in that water (with nitrates) are removed over winter as the tanks are drained due to rainfall (approx 1000l over april to August over the surface area of the trank) or water taken out and used for other purposes? I would imagine that the volume of water removed could have a significant affect on the concentation of nitrates.

While chasing up some research material today I came across a reference that stated that the recommended maximum nitrate level for trout was 1,000 ppm. That would go some way towards explaining why high nitrate levels are not causing trout deaths.

There was some other good info but I left the copy at work. Now if only I could find it again

My FT only overflowed once, water was occasionally removed for watering the dirt garden. I don't keep my FT full to the brim like many people do, at start of winter I think I had about 600L in there. I havent added water myself to the system in many, many months. Even after the recent rain here, I've still only got 850L in the FT. I'm on the iPad now, I've got my water level measurements on the PC if you're really interested.

Lots here: http://www.google.com.au/search?q=maximum+nitrate+trout

OK guys, I have looked into this and without getting into NOEC or LC50s it seems that the recommended maximum nitrate nitrogen level of 1,000mg/l or about 4400ppm (mg/l). That's massive
However they go on to say

So it seems that if we keep our nitrate levels down to below 400ppm the trout should be fine and not impeded by the nitrates. And if they get up into the 1000s the trout should not die but may not grow as fast and you really do need to plant more veggies.

Lower nitrate levels apply to fry but that is not really of any concern to us.

OK I can't resist the LC50 over 7 days for trout fingerlings @ 13 to 14C was 1061mg/l of nitrate nitrogen (about 4700ppm or mg/l of nitrates)

The NOEC (no observed effect concentration) for trout fry over 30 days @10C was 2.2mg/l of nitrate nitrogen (about 10ppm or mg/l of nitrates)
So there you have it

Yep, trout seem to often be more susceptible to things than other species.... especially the "fry" for some reason...

In the case of nitrates... probably because in nature they're used to fast flowing, heavily oxygenated... clean ... nitrate free... streams...

even at 4000ppm for nitrates is, at least to me, very high. I was getting worried when mine hit 800ppm. All that worry for nothing

I couldn't imagine any of our systems getting anywhere close to those levels nor should they.

Bluegil tolerate twice the level of nitrates - 8000ppm.

make that 9300ppm of nitrates for bluegill. Too late at night for me to be doing math in my head

Even given the nitrate tolerances.... I still don't think it's good to run a level of nitrogen loading.. of 800ppm.. in an AP system...

The hetrotrophic bacteria must be sucking the life out of the oxygen content in the system....

Frankly... I just can't understand how it's even possible to get to that level....

Unless the system is totally unbalanced... and/or overstocked....

Either way... i still think it's a catastrophe waiting to happen...

28 Trout and 100 Silvers (that were hardly feeding) in a 5 bed 3000l of filtration and 5000l of water system is hardly overstocked. A 5 bed (2500l of filtration) BYAP system is recommended to have 25 fish per bed so I could have had 125 trout and be appropriately stocked.

The trout were slightly overfed (thanks Gavin) but the SP were hardly feeding (less than a tablespoon per week). The trout at the time were 750gms and growing well, ammonia at 0,25 Nitrites at 0 , the beds well planted, so it is hard to follow why the system would be unbalanced.

If the catastrophe is waiting to happen it is taking its time.

IMO it was winter and cold and the capacity for the plants to use the nitrates produced was less than the amount produced. Therefore they increased.

The only recent problem was the increase in ammonia to 0.5 when I adjusted the pH up. The drop in pH caught me by surprise as I have 2kg of small shells in the system and about 300gms of crushed limestone.

In my experience people would not routinely test for nitrates once their levels get over 160ppm as that is the limit of the test and you have to undertake some reasonable level of dilution that is accurate to get any meaningful results.


I take your point above but if you could explain it further. Why would the heterotrophic bacteria suck more oxygen out of the system at 800ppm of nitrates than at say 200ppm of nitrates given the same level of food inputs and fish load?
The article I cite above infers that the recommended maximum nitrate nitrogen level of 1,000mg/L (4400ppm of nitrates) in a recirculating aquaculture systems. Surely they would have similar oxygen issues at such high recommended levels of nitrates?

I'll get back to you


The vast majority of people just wouldn't even approach those levels...


I'll get bqck to you


That's the recommended MAXIMUM tolerable rate..... I can bet my last dollar.... that anyone running a RAS system.... would not even let their system come to even probably 100-200....

Precisely for oxygenation, and general management reasons...

I have looked for data from systems operating over winter with trout and there is not much about. Charlie however reported a level of 300ppm for 30 SP, 5 trout and a handful of yabbies and marron.
Also had my tanks and all my grow beds been outside I would have had at least sufficient water input from rain for a 100% water change over winter so that would have reduced the nitrate levels as with any system operating outside.

Rupert I completely agree with you that we should not let our systems get beyond 400ppm for nitrates if we want good growth and healthy fish
Facts - Nitrates greater than 440 ppm appear to result in sublethal effects to rainbow trout.
Rainbow trout growth does not appear to be inhibited by nitrates less than 440 ppm.
Nitrates of approximately 1800ppm with maximum levels of 2600-3000 ppm results in increased mortality and behavior that indicates severe stress.

So while the high nitrates wont kill them quickly, should those levels be reached we should make every effort to reduce the level down to below 400 to 500ppm.

I had a quick look back through my thread, as you do, and found that I was missing the additions to the system I put in in April for the trout - better late than never

So here goes - Think March of 2012. I had the 1000l tank since day 1 and it sat outside growing tadpoles and mozies until I could find the time to get it in place. With the trout season not too far away I finally got it in place and rerouted all my drain pipes.

Below is the main tank earlier in the year. It houses my Silvers and is 4000l in size. All the air lines are run down from the main above the tanks. Keeps them out of the way and allows them to be moved easily. The white bar across the top is a spray bar for aeration if the power goes off and to keep the water circulating. It also goes to the piping on top of the sump so even if the power goes off the water is moving between both the tanks. This has helped keep the ammonia down when we had a 3 hour outage while I was at work. Second thing I did when I got home was to test both tanks - results - both were the same.
The floating rafts have bok choy, english spinach, silverbeet and cabbage. The cabbage and spinach was a fail, the bok choy did ok and the silverbeet grew as well as in the grow beds


This is the sump tank with the trout. Of my 5 grow beds, 2 empty into the sump and the other 3 can be simply turned and redirected into the sump if necessary. In this photo there are 3 returns into the sump, the third runs to the pump outlet in the centre of the tank. Note the high tech system for holding the net covering the tank in place. I knew the offcuts from the deck would come in useful